The present invention relates to a discharge lamp lighting apparatus, which can be suitably used, for example, as a light source for a projector apparatus, an exposure apparatus etc.
A short arc type discharge lamp, in which a pair of electrodes is arranged so as to face each other in an arc tube, may be used as a light source of a projector apparatus, an exposure apparatus etc. Japanese Patent Application Publication No. 2009-193768 describes such a discharge lamp with electrodes that each comprise an electrode head portion and an electrode axis portion that are integrally formed with each other by cutting and a coil that is wound around the electrode head portion. Japanese Patent Application Publication No. 2005-19262 describes a discharge lamp with an electrode in which a coil portion is formed by melting a coil wound around an electrode head portion. Moreover, Japanese Patent Application Publication No. 20010-165661 describes a discharge lamp with an electrode in which a cylindrical portion whose outer diameter is the same as a diameter of a back end of an electrode head portion is formed on a back end face of the electrode head portion.
However, as to these discharge lamps, if the lamp is lighted for a long time, there is a problem that damage such as a crack and an electrode crease, etc. arises in, for example, part of an electrode axis portion, which projects in the arc tube.
However, as a result of the inventors' earnest examination into the causes of such damage of the electrode axis portion, it turns out that vibration of the electrode is generated by a ripple in alternating current supplied to such a discharge lamp, so that the electrode axis portion is damaged.
Specifically, as shown in FIG. 11A, an electrode 95 of a discharge lamp has an electrode head portion 96, which is formed at the tip of an electrode axis portion 97, and a base end portion of the electrode axis portion 97 is buried and held in the sealing portion 92 of the arc tube 90, so that the electrode head portion 96 may be arranged so as to be located in the light emission section 91 of the arc tube 90. Since the mass of the electrode head portion 96 is fairly larger than that of the electrode axis portion 97, when the electrode 95 vibrates in a state where alternating current is supplied to the discharge lamp to be lighted, as shown in FIG. 11B, a portion of the electrode axis portion 97, which projects in the arc tube 90, is elastically deformed. When this phenomenon is repeated for a long time, damage such as a crack, an electrode crease, etc. arises in such a portion of the electrode axis portion 97. The present inventors examined the relation between the characteristic of alternating current supplied to the discharge lamp and the damage of the electrode 95, and found out that when the frequency of ripple of the alternating current is close to the natural frequency of the electrode 95, such damage tends to occur in the electrode 95, and the larger the power of ripple of the alternating current, the more such damage tend to occur in the electrode 95.